chore(main): add lint workflows and configs

.github/workflows/lint.yaml

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+name: Lint
+
+on:
+  pull_request:
+    branches:
+      - "main"
+    paths:
+      - ".github/workflows/lint.yaml"
+      - ".github/yamllint.yaml"
+  schedule:
+    # Run at 00:00 every day.
+    # Ref: https://man7.org/linux/man-pages/man5/crontab.5.html
+    - cron: "0 0 * * *"
+  workflow_call:
+
+env:
+  # chisel-releases branches to lint on.
+  RELEASES: ${{ toJson('["ubuntu-20.04","ubuntu-22.04","ubuntu-23.10","ubuntu-24.04"]') }}
+
+jobs:
+  prepare-lint:
+    runs-on: ubuntu-latest
+    name: "Prepare to lint"
+    outputs:
+      matrix: ${{ steps.set-output.outputs.matrix }}
+    steps:
+      - name: Set output
+        id: set-output
+        run: |
+          set -ex
+
+          if [[
+            "${{ github.base_ref || github.ref_name }}" == "main" ||
+            "${{ github.event_name }}" == "schedule"
+          ]]; then
+            echo "matrix={\"ref\":${{ env.RELEASES }}}" >> $GITHUB_OUTPUT
+          else
+            echo "matrix={\"ref\":[\"\"]}" >> $GITHUB_OUTPUT
+          fi
+
+  lint:
+    runs-on: ubuntu-latest
+    name: "Lint"
+    needs: prepare-lint
+    strategy:
+      fail-fast: false
+      matrix: ${{ fromJson(needs.prepare-lint.outputs.matrix) }}
+    env:
+      main-branch-path: files-from-main
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ matrix.ref }}
+
+      - name: Checkout main branch
+        uses: actions/checkout@v4
+        with:
+          ref: main
+          path: ${{ env.main-branch-path }}
+
+      - name: Install dependencies
+        run: |
+          set -ex
+          pip install --upgrade pip
+          pip install yamllint
+
+      - name: Lint with yamllint
+        env:
+          config-path: "${{ env.main-branch-path }}/.github/yamllint.yaml"
+        run: |
+          set -e
+          yamllint -c "${{ env.config-path }}" \
+            chisel.yaml \
+            slices/
+
+      - name: Lint with SDF-specific rules
+        run: |
+          set -e
+
+          export LC_COLLATE=C
+          EXIT_CODE=0
+
+          err() {
+            echo "error:   " "$@" >&2
+            EXIT_CODE=1
+          }
+          warn() {
+            echo "warning: " "$@" >&2
+          }
+
+          for filename in $(find slices/ | grep "\.yaml$" | sort); do
+            yq '.slices | keys | .[]' "$filename" | sort -C || \
+              warn "$filename: slice names are not sorted"
+            for slice in $(yq '.slices | keys | .[]' "$filename"); do
+              key="$slice" yq \
+                '.slices | with_entries(select(.key == env(key))) | .[].essential[]' \
+                "$filename" | sort -C || \
+                err "$filename: $slice: \"essential\" entries are not sorted"
+              key="$slice" yq \
+                '.slices | with_entries(select(.key == env(key))) | .[].contents | select(.) | keys | .[]' \
+                "$filename" | sort -C || \
+                err "$filename: $slice: \"contents\" entries are not sorted"
+            done
+          done
+
+          exit $EXIT_CODE

.github/yamllint.yaml

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+# yamllint configurations.
+# Ref: https://yamllint.readthedocs.io/en/stable/configuration.html
+
+extends: default
+
+# Ref: https://yamllint.readthedocs.io/en/stable/rules.html
+rules:
+  braces:
+    forbid: false
+    min-spaces-inside: 0
+    max-spaces-inside: 1
+    min-spaces-inside-empty: 0
+    max-spaces-inside-empty: 0
+  brackets:
+    forbid: false
+    min-spaces-inside: 0
+    max-spaces-inside: 1
+    min-spaces-inside-empty: 0
+    max-spaces-inside-empty: 0
+  comments:
+    level: error
+  comments-indentation:
+    level: error
+  document-end:
+    present: false
+  document-start:
+    present: false
+  empty-lines:
+    max: 1
+  indentation:
+    spaces: 2
+  line-length:
+    max: 80